For most of the series, the Wise Ones were really underused as a fighting force for no reason besides that it would've have made things too easy for Rand and the Light side.

I mean at the start of LoC Rand had thousands of them available yet he was all "I need the Asha'man otherwise I have no chance against the Tower. He didn't have any of them guarding his back when meeting with Elaida's representatives. he didn't take any besides Aviendha when he went after Rahvin. Even after Dumai's wells which showed the traidition of them staying out of battle is over, he never used anywhere. Not against Samail, not against the Seanchan, not even when the Asha'man renegades attacked him and made him really distrustful of the Asha'man in the end of PoD and he needed someone to guard his back at the Cleansing and help him kill Rochaid and company.

Besides, given how overpowered channellers are compared to normal people, the normals would've been just cannon fodder if there were thousands of channellers on both sides. Which is something Jordan clearly didn't want since he spent so much pages on Perrin, Elayne, Rand, etc, gathering big conventional armies and preparing them for the LB.